The wish to raise the quality of a software is hardly much older than the software development itself. At the beginning, a set of rules should be determined which define software development guidelines, especially in major projects with multiple developers. Fortunately, PLCopen published recently a draft specifically for IEC 61131-3.
If instances of a function block have to be created, the exact type of the function block should be known before compiling. Properties of an application can hardly be expanded by this fixed assignment. For example, this will be the case when the function block is located in a library and the access to the source code is thus not possible. The instance variable is constrained by a specific type. A class factory can help to break these stiff structures.Continue reading “IEC 61131-3: The Abstract Factory Pattern”
While the notion of inheritance is used readily and frequently, interfaces are rather rarely applied. However, interfaces provide a number of benefits, which increase flexibility of the PLC programs and improve maintenance. The following post will introduce the possibilities of interfaces relating to the IEC 61131-3 standard.